Air springs are widely used on vehicle suspension systems since they generally result in a lower system spring rate and a lower vehicle natural frequency than other available types of springs. A low spring rate and low natural frequency result in superior isolation of road-induced disturbances and improved contact between the wheels and road surface (in other words a better ride). Unfortunately, decreasing the spring rate also decreases roll stability and increases suspension travel, both of which can be a negative feature in some applications.
A number of methods have been employed to overcome this trade-off. Many suspensions employ a bump-stop to limit axle travel and body roll. However, when the bump-stop is contacted very high loads are transmitted directly into the vehicle frame resulting in undesirable harshness. Other designs have made use of costly valves or control units to vary the spring rate and natural frequency.
The present invention provides an innovation in air springs when used in suspensions, particularly for heavy duty trucks and trailers. The air springs of the invention have dual volumes, one being a compressible variable chamber and the other being a fixed volume chamber. The interiors of the two chambers are separated by a partition which has an orifice therein providing air or gas flow communication between the chambers. A post-like orifice closer or plug is mounted within the compressible variable volume chamber for closing the orifice during jounce action of the associated suspension. The post-like closer has a deformable or resilient portion which has a low spring rate and a relatively rigid portion which has a high spring rate. During a jounce of the associated suspension of sufficient severity the deformable portion of the post-like orifice closer engages and closes the orifice thereby isolating the fixed volume chamber from the variable volume chamber. In the event of a sufficiently severe jounce the rigid portion of the post-like closer comes into play and arrests further jounce movement.